A polyether polymer having a high molecular weight obtained by polymerizing a cyclic formal using a cationic catalyst is generally soluble in warm water, and has fluidity at a temperature relatively close to room temperature despite having a high molecular weight, and can be processed into a flexible film. Therefore, as a use of the polyether polymer utilizing this feature, a number of uses, such as a packaging material, a fiber treatment agent, a thickener, a plasticizer, and further a heat transfer medium and a lubricant, are considered.
With respect to the method for producing a high molecular-weight polyether polymer, a method using 1,3-dioxolane as a main monomer and a composite polymerization catalyst comprising a heteropolyacid and a carbonyl compound has been described (see, for example, Japanese Unexamined Patent Publication No. Hei 7-41532). The use of a catalyst containing only a heteropolyacid requires a prolonged polymerization time and further cannot satisfactorily increase the number average molecular weight, and, when the amount of the catalyst used is increased, the temperature in the polymerization system is rapidly increased, so that the resultant polymer has a lowered molecular weight. Therefore, the use of a composite polymerization catalyst is considered effective in the above method. Further, there have been described a method in which 1,3-dioxolane and trioxane are subjected to copolymerization while controlling the temperature during the polymerization so as not to be too high to obtain a high molecular-weight polymer (see, for example, Japanese Unexamined Patent Publication No. 2003-246857) and a method in which 1,3-dioxolane and 1,3-dioxepane are subjected to copolymerization (see, for example, U.S. Pat. Nos. 5,166,224 and 5,412,042).